Conventionally, a hydraulic pressure braking force generating device is known which applies a hydraulic pressure braking force to a vehicle wheel corresponding to a wheel cylinder by supplying the wheel cylinder with a brake fluid from the master cylinder. Generally, when a hydraulic pressure in a wheel cylinder (hereinafter referred to as “wheel hydraulic pressure”) increases, a pair of brake pads corresponding to the wheel cylinder is brought into contact with a brake rotor and then the brake pad is pushed onto the brake rotor by the wheel pressure to perform an effective braking operation by the braking force. When the pressure is not generated in the wheel cylinder, the brake pad and the brake rotor are naturally separated from each other. Accordingly, until the brake pad is brought into contact with the brake rotor, the braking force is not effective to the brake performance in spite of the depression operation of the brake pedal by an operator of the vehicle. Accordingly, there is still a room for improving accuracy in change of braking force relative to the brake operation (hereinafter referred to as a “responsiveness of braking force”).
Therefore, in order to improve the responsiveness of the braking force, a pre-charge technology has been developed and proposed, for example, for a brake control device disclosed in JP 2004-161174 A (Patent Literature 1) in which a predetermined pressure is applied in the wheel cylinder in advance. According to this technology, by obtaining the wheel hydraulic pressure (brake pressure) using a pressure sensor, a predetermined pre-charged pressure has been generated in the wheel cylinder.